move the hard coded URL in tt file to POST a form

If you want to move any element from the template to the module, it's quite a simple matter of assigning it to a stash variable:

$c->stash('action' => 'http://example.org/cgi-bin/download.pl');
[download]

<form action="[% action %]" method="POST">
[download]

However, for a better answer to your case, I suggest showing the template code as well, and maybe some more information about the task in hand.